New evidence indicates that distinct mutations cause familial Parkinson's disease (PD) by mechanisms that may also operate in sporadic PD. During the current funding period we have identified cellular dysfunction without cell death in mice expressing various mutations known to cause PD in humans. In this renewal application we will test the hypothesis that common mechanisms of dysfunction may be induced by distinct mutations and offer therapeutic targets for treatment at early stages of the disease, before further cell death causes irreversible damage. Project 1. 2. and 3 form the continuation of the current award and will continue to use a multidisciplinary approach to uncover the mechanisms of neuronal dysfunction in existing and novel mouse models. In specific aim 1 of project 1 we will determine the progression of behavioral deficits and neuropathology in already available mice overexpressing alpha-synuclein under different promoters and parkin KO mice. We will use a battery of sensitive motor tests we have developed to assess the motor phenotype of the mice, and will extend this analysis to non-motor behaviors because related symptoms can have a major impact on patient quality of life, as examined in project 5 of the Center. We will use immunohistochemistry to determine the progression of alpha-synuclein pathology and glial activation throughout multiple brain regions known to be affected in PD, and to detect anomalies in the expressionof proteins involved in neurotransmitter release and examined in project 4 of the Center. We will use ligand binding and molecular approaches to identify dysregulation of dopaminergic transmission that will befurther examined with neurochemical approaches in project 2 and with electrophysiology in project 3. Finally, eventual cell loss in brain regions that are affected in PD (locus coeruleus, ventral medulla, nigrostriatal dopaminergic neurons) will be assessed in older animals with unbiased stereology. In specific aim 2, we will extend this analysis to novel mouse models generated in the Mouse Genetics Core with state of the art BAG technology. These include a mouse model expressing a parkin mutation shown to cause the loss of dopaminergic neurons in Drosophila. These mice will be characterized with the same methods described above, before being further analyzed in projects 2 and 3. Studies in project 1 will parallel longitudinal clinical studies of project 5 that examine disease progression in PD patients, including psychiatric and cognitive co- morbidity. They will provide critical information on the time course of the deficits and new models for projects 2 and 3 and test in an in vivo mammalian system the hypotheses generated in cellular models in project 4 of the Center.